A timing belt, timing chain or cambelt is a part of an internal combustion engine that synchronizes the rotation of the crankshaft and the camshaft(s). The engine’s valves open and close at the proper times during each cylinder’s intake and exhaust strokes.
What will happen if the it breaks ? If the timing belt snaps they run into each other causing bent valves. Most common cylinder head or camshaft damage, and possibly piston and cylinder wall damage. While it is possible that no damage could occur from a snapped belt on an interference engine, such a case is unlikely.